[Webkit-unassigned] [Bug 268071] New: The usage of flat qualifier breaks the WebGL context in Safari

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=268071

            Bug ID: 268071
           Summary: The usage of flat qualifier breaks the WebGL context
                    in Safari
           Product: WebKit
           Version: Other
          Hardware: iPhone / iPad
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: WebGL
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: endanke at gmail.com
                CC: dino at apple.com, kbr at google.com, kkinnunen at apple.com

We have run into a regression regarding the usage of the "flat" storage qualifier in GLSL shaders, which causes the browser to lose the WebGL context across several tabs. 
This breaks rendering of any further WebGL content and to recover, the browser needs to be force-closed and opened again.

The issue was reproducible in Safari on multiple iPad models (MK2K3KN/A and MQDW2TY/A) on one iPhone model (MT9G2ZD/A) and across different iOS versions (16.3.1 and 17.3).
On desktop environment we were unable to reproduce it.

The exact conditions are not clear, as the browser can render some frames before it loses the context, but usually it happens within a couple of seconds.

As a minimal example, we've set the following property in a vertex shader:

flat out float v_test;
...
v_test = 1.0;

And accessed it in the fragment shader similar to:


flat in float v_test;
...
float alpha = v_test;
glFragColor = vec4(1.0, 1.0, 1.0, alpha);

The repeated usage of these shaders breaks the context in a couple of seconds.

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